Ultrasonic assembly improves reliability

Ultrasonic technology reliably and consistently bonds reservoir jugs for humidifiers and other household appliances made by Lasko Products, West Chester, Pa. The company previously used solvent bonding, but glue did not make an airtight seal, leading to a high failure rate.

"Gluing was sloppy, time consuming, and involved excess handling of plastic parts," explains Ralph Zwakenberg, Lasko's industrial design manager. "We needed to speed up the process, so we tried ultrasonic bonding." Sonobond Ultrasonics, West Chester, Pa., which makes ultrasonic welding equipment for textiles, metals, and plastics, designed a customized unit for this specific application.

Sonobond's machines transmit vibrational energy to overlapping plastic parts. This softens the plastic material in a fraction of a second. When the material resolidifies, the bond is made. "Because of the size of the finished product, Lasko needed a machine with dual welding heads," explains Kyle Kimbro, vice president of Sonobond. "We also adapted the welder to accommodate the different jug configurations, added soundproofing, and put in an enclosure to further reduce noise."

Sonobond's SureWeld equipment uses a highly stable bench press mounted on a rectangular support column which minimizes deflection when pressure is applied. According to Kimbro, these features are critical in the precision welding of rigid plastic assemblies. "The SureWeld machine gives repeatable accuracy, while it aligns welded parts."

Replacing gluing with ultrasonic bonding let Lasko reduce setup times and the testing phase. And because welds are so reliable, Lasko has been able to cut down on other testing as well.